rOL. XXIV.] PHILOSOPHICAL TRANSACTIONS. 227 



aperture without any friction ; also the air, which has been first driven and re- 

 moved from the wing, cannot lose its swiftness, because the wings, which con- 

 tinually follow, always drive new air, keeping that which is before always in the 

 same velocity. This new shape of the Hessian bellows affords also another 

 advantage; because the air in going round follows the spiral line, which is; 

 nearer to the straight line than a circular circumference; and when the air 

 comes to the aperture, it gets into it without any loss of its substance; but in 

 the cylindrical machine, fig. l6, the air always goes round in a circular circum- 

 ference ; and when it comes to the aperture, the wind is driven exactly in the 

 direction of the tangent, except just in the beginning at c; and afterwards the 

 impulse is oblique; which obliquity is always increasing till the wing comes to 

 the point a, and must occasion a great dimunition of its strength. I have 

 made such bellows where the radius ap is but lO^ inches, the wing Am 2 inches 

 broad, and 9 inches high; because the tympanum is also so high, or little more: 

 the aperture ab was also Q inches, or a little more; so that it makes a square 

 hole. When I work this engine with my foot, it makes such a wind as to 

 raise up 2 pounds weight; and a stronger man could do much more : but this 

 is more than sufficient for our purpose, since we need only drive air enough for 

 the respiration of such men as can work in the mine; and we can easily make 

 wooden pipes with boards, to conduct the wind to the very bottom: so that the 

 air within will be continually renewed, as well as without. 



I have made some trial of the Hessian bellows in a very strong fire in a fur- 

 nace, to melt glass, iron, or any other hard metal ; and though I could open 

 the furnace above the matter to be wrought upon ; yet no flame would get out 

 through the aperture, nor could cold air from without get into the furnace : so 

 that it is very like this will be a great conveniency for several sorts of work, 

 since men may work the matters when they are most softened in the fire ; and 

 they may be drawn up perpendicularly, so as not to be bent, as they are when 

 drawn horizontally. I believe this would be a good way, especially to make 

 glass pipes and looking-glasses of an extraordinary size. And I think that the 

 Hessian bellows may be applied to several good uses, and so deserve very much 

 to be improved. 



How to judge of the Age of Manuscripts, the Style of Learned Authors, Painters, 

 Musicians, &c. By Mr, Humfrey Wanley, N° 300, p. IQQS. 



It is evident that a man may judge of some manuscripts by the hand-writing ; 

 and of the genuine and spurious works of some authors, and the time in which 

 they lived, by their style, but can scarcely be infallible : suppose for instance, a 



G 6 2 



